134 NATURAL SCIENCE. Aug.. 



rating effect of the aquatic medium in which the ancestral endogens 

 originally and primarily grew." 



A large part of the remainder of the paper is devoted to evidences 

 furnished by the order Nymphaeaceae, which is remarkable for having 

 many points of agreement in structure with endogens, and, as it is 

 aquatic, may be looked to in support of the theory. 



As regards the embryo, some abnormal cases of the yellow water- 

 lily [Nuphav liiteiim) described by Hegelmaier are cited, where the two 

 cotyledons were more or less united, and the two halves very unequally 

 developed. These are quoted as "an important and independent 

 witness to the gradual arrest of one cotyledon." It seems rather a tera- 

 tological phenomenon likely to occur anywhere. 



In discussing the arrest of the primary root, Mr. Henslow is, we 

 think, clearer, and adduces what is, at first sight, a more promising 

 piece of evidence. A very characteristic feature of monocotyledons 

 is the disappearance of the primary root, that, namely, produced by 

 elongation of the radicle of the embryo, and the subsequent develop- 

 ment of adventitious roots. Now this also obtains in Nymphaeaceae, 

 aquatic umbellifers, and other water-loving exogens. Hence the argu- 

 ment that its presence in endogens which to-day are not aquatic, 

 e.g., grasses, is due to inheritance from aquatic ancestors. It must, 

 however, be remembered that fibrous roots occur in exogens which are 

 not aquatic, and as regards the grasses, one of the largest orders of 

 Angiosperms, when we remember their habit, and how they frequently 

 grow in loose soil or dry exposed situations, the spreading fibrous root 

 seems to meet the case so perfectly that the hypothesis of an aquatic 

 ancestry appears unnecessary. Following a suggestion of Mirbel's, 

 the author explains the arrest of the primary root in endogens as 

 follows. When the cotyledons are raised above ground and act as 

 leaves, they can maintain the existence of the tap-root and enable it 

 to grow until the foliage of the plumule is sufficiently developed to 

 carry on the work. If the cotyledons remain below ground, " the 

 plumule at once develops its leaves perfectly, as in the oak, and its 

 foliage can then nourish the tap-root instead of the cotyledons doing 

 so." In submerged aquatic plants the first leaves are more or less 

 rudimentary, and, " being under water, their assimilating powers are 

 greatly impeded," so that the primary root perishes for want of 

 nourishment. 



Now, as a matter of fact, as Sir John Lubbock points out in his 

 "Seedlings" (p. 356), when the cotyledons remain beneath the ground 

 the plumule does not, as a rule, ^^ at once develop its leaves perfectly," 

 but the primary ones are reduced to scales, often passing gradually 

 into the form of the adult leaf. This happens in the oak, and the 

 tap-root is nourished, not by the plumule, but by the fleshy cotyledon, 

 which also suppHes nutriment for the growth of the stem. In this 

 way the first green foliage leaves are borne well up in the air and 

 raised above the humus, dead leaves, etc., which might have buried 



